The CAS Registry Mumber 74971-65-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,9,7 and 1 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 74971-65: (7*7)+(6*4)+(5*9)+(4*7)+(3*1)+(2*6)+(1*5)=166 166 % 10 = 6 So 74971-65-6 is a valid CAS Registry Number.